Some mining machines, such as those presently used in coal mines, have rotating wheels or drums provided with numerous bits. These wheels or drums are equipped with bits which are driven against the seam of coal or other mineral to be extracted, and the bits penetrate the coal, mineral or other rock, breaking it up so that it can be removed. Although the bits are usually provided with a point made from hard metal alloy such as tungsten carbide, the bits wear quickly because these bits continually impact minerals and the surrounding substrate. Frequently, the softer steel in which the hard point is inset wears away and the exposed point simply pushes out or breaks off. Thus, the bits have been designed to be replaceable. During typical operations in a coal mine for instance, the bits on the miner have to be replaced twice in an eight hour shift. And, if harder rock is encountered, replacement must occur even sooner. The mining machines typically have as many as 180 bits, and it presently takes nearly an hour and a half to replace them.
The bits are of two types: the first type, often referred to as a tri-type bit has a conical head on the cylindrical shank. The second type of bit, often referred to as a pencil bit, is generally cylindrical with a front tapering to a point.
The bits are inserted into the blocks at the optimum cutting angle, and the blocks are mounted to rotating drums or wheels on the miner. The most common type of block is the tri-type block, such as that manufactured by the Joy Manufacturing Company. These blocks have a generally cylindrical bore with an open breach end. The shank of the bit is received in the bore with the back end of the bit protruding through the open breach end.
In the tri-type bit axial loads from impacting the rock are borne by the shoulder on the bit at the abutment of the head and shank, which engages the block. In the pencil type bit, axial loads are supported by an abutting surface provided at the back of the block in alignment with the bore.
It is important that the bits be securely mounted in the blocks. Each bit weighs approximately a pound and is a very dangerous projectile if it flies off the rotating wheel or drum. However, as just discussed, the bits must be removable for replacement. In addition, the bit must be allowed to rotate in the bore so that the bit wears evenly and dust is prevented from caking in the bore and wedging the bit permanently in the block.
Before this invention there was no fast and secure way to rotably mount a bit in a block. A number of methods of engaging the bits are disclosed in Krekeler, U.S. Pat. No. 3,397,012 and Krekeler, U.S. Pat. No. 3,397,013 both issued Aug. 13, 1968. The most common way to mount the bit was to provide a circumferential groove around the shank of the bit near the end, so that the groove would be exposed at the open breach end of the block. A heavy gage wire hose clamp was then expanded with a pair of pliers and the clamp slid over the end of the shank into the groove, wherein it was allowed to close. The clamp in the groove prevented the bit from sliding out of the block.
The hose clamp mounting, although heretofore the best available and most widely used method, presented numerous problems. The clamp was hard to manipulate, especially in the confined breach opening in the block. Each worker had to carry special pliers to operate the clamps, as well as a supply of spare clamps which were easily lost. The dark, dusty underground environment compounded the problems of using the clamps, since the only light to work by was from the workers helmet. The result was that it would take nearly one and one half hours to change the over 180 bits on a typical mining machine. Because causing delay, the difficulties with installing the clamps often resulted in a bit being improperly secured, so that during use it could fly out of the block.
Emmerich U.S. Pat. No. 4,026,605 discloses a double ball retainer on the shank of the bit that is received in an annular groove in the back of the block. This was not the tri-type of block now most commonly used, and to which the present invention herein relates. As that patent states, prior to the double ball retainer most retainers were mounted in the bore of the block, for example sometimes a circular retainer, known in the art as a "wedding band" was carried in an annular groove in the rear of the block.
In Emmerich, the balls had to be retained in the bit above their equator, and this left little surface to engage the block and resist outward motion of the bit. This was at least partially intentional because there was no access to the interior of the block, meaning that the bit had to be removable by pulling on the bit. It was not uncommon for the head of the bit to shear off during service and the shank become stuck in the bore. To prevent failure in removal, there had to be minimal resistance to outward motion. This was totally inconsistent with safety because a mounting method which allowed bits to be easily removed would also let a bit fly off during use. Another problem was that special tools were needed so that a worker could engage the head of the bit and drive it free from the block.
After a while in service, the annular groove in the block would wear, making it even easier for the bit to escape. Furthermore, dust working its way down the bore between the bit and bore would collect in the annular groove and facilitate a camming action urging the balls out of engagement with the block. Thus, the Emmerich device was wholly unsatisfactory for use in the tri-type blocks. For safety's sake, the bits must be securely mounted in the block. The rounded ball retainer simply did not achieve this, for so long as they could be jerked free it was not sufficiently secure. What was needed was a way to releasably secure the bit cooperating with the open breach end, and easily assessible therefrom. This brings up another failing of the double ball retainer, in that if one ball was accessible, the other wasn't and the bit could not be released if the balls achieved a truely secure engagement. Thus, until this invention, the only way to mount bits to the tri-type blocks was the cumbersome hose clamp method.
Still another disadvantage with the Emmerich device was the close fit machined surfaces required to mount the retaining device in the shank of the bit. As can be appreciated, there can be quite a number of bits in a mining machine, and their useful life may be less than a shift in the mine. Thus, the expense involved in manufacturing a bit is critical in determining its applicability. These machined surfaces to close tolerance can be achieved only at a significant expense which increases the cost of each bit.
The present invention provides a bit that is easier to install and remove from the blocks, and thus makes replacement faster and more reliable. The bit is provided with an insert having a spring-loaded cylindrical button extending radially from the shank near the rear of the bit. A rough drilled hole can be made in the shank, and the insert secured in the hole with an epoxy or other adhesive, thereby eliminating the machining expense of prior art devices. The button is compressible so that the bit can be inserted through the bore in the block. When the button passes beyond the breach opening in the block it extends outwardly, and the sidewall of the button engages the end of the bore in the block preventing the bit from sliding out of the bore. The button may, with some effort, be depressed by the worker so that the bit can be slid from the bore. However, since it is a flat side which is engaging the block, there is no camming action or other force tending to depress the button during operation. The worker needs no special tool or extra parts to mount or remove the bits. Removal and installation of the bits is greatly simplified so that despite the difficult environment, the bits are securely mounted and fly off incidents are virtually eliminated. The result is that a job that used to take nearly one and one half hours can be accomplished in less than half the time.
The present invention, therefore, makes the mine environment safer by more reliably engaging bits in the blocks. Furthermore, it causes a substantial savings because it reduces the down time of the mining machine and the other equipment waiting on the miner to mine coal. Since the mining machine can mine as much as ten tons of coal in 30 seconds, every minute saved is important. With the present invention the increased safety and efficiency are achieved at reduced cost over prior art devices.